584 ADAM SEDGWIOK. 
loose mesh, and its fibres are always delicate; and it is no 
doubt often torn and destroyed by the preserving processes to 
which the embryo has to be subjected. But delicate as it is, 
there can be no doubt of its existence in Vertebrate embryos ; 
and there can be no reasonable doubt that it is derived from 
the processes and strands left between the cells as a result of 
the incomplete cleavage of the ovum. There can be no doubt, 
I say, that the network exists; but that the peripheral nerve- 
fibres and the central nerve-fibres are derived from it has not 
yet been shown. That is the point which now needs investi- 
gation, and I hope myself to treat of it in a future paper. 
Meanwhile I may say that there is in my opinion evidence 
to show that the whole of the nervous connections (by nerve- 
fibres and otherwise), both in the central organ and at the 
periphery, are developments of this pre-existing network, which 
connects together at all times the whole of the cells derived 
from the fertilised ovum. 
I do not dispute for one moment the description given by 
Dohrn! of the structure of particular stages in the development 
of a nerve-fibre ; but in saying that it consists of a row of ecto- 
derm-cells laid on end to end he is, I think, going beyond his 
facts, being led to such au interpretation of the appearances 
not so much by observation of previous stages as by a process 
of reasoning based upon the cell theory of structure, which 
theory implies that the animal body at one stage of its onto- 
geny consisted of cells which are separate from one another 
and only secondarily fuse to form the adult tissues and com- 
binations. 
1 ¢Studien z. Urg. d. Wirbelthierkorpers,’ No. 17. 
